Arthrodesis is surgery for the purpose of almost completely eliminating the mobility of a joint by giving rise to “bone fusion”. Such surgery can be necessary when the patient is suffering from severe and final arthrosis.
To perform such surgery, it is known to make use of arthrodesis apparatus comprising firstly an arthrodesis nail that is to be implanted within the joint, and secondly an instrument for putting the arthrodesis nail into place.
The arthrodesis nail is generally inserted into housings formed in succession through the various bones making up the joint, and the arthrodesis nail includes fastener holes that are designed to cooperate with fastener screws in order to secure the arthrodesis nail with the bones forming the joint.
In order to put such arthrodesis nails into place, it is known to use an instrument including compression means to move together the bones forming the joint and, for example, with an ankle joint, serving to bring the calcaneus closer to the tibia.
The compression step is very important in the surgery, insofar as this step determines the relative positioning of the bones constituting the joint, and poor positioning can constitute a difficulty for the patient.
Unfortunately, with the ankle joint the compression means are generally implemented with the help of a bearing surface arranged to bear against the heel and suitable for being moved in order to exert pressure thereagainst so as to move the calcaneus and the tibia closer together.
The operating technique generally used is as follows:                the surgeon uses a fastener screw to secure the arthrodesis nail to the tibia;        thereafter, the surgeon moves the bearing surface so that it comes to bear against the heel and compresses the joint, thereby moving the tibia and the calcaneus closer together; and        finally, the surgeon secures the nail to the calcaneus while maintaining the pressure exerted by the bearing surface against the heel.        
Although arthrodesis apparatus in the prior art are advantageous in terms of preventing the joint from moving, the arthrodesis apparatus, nevertheless, suffers from drawbacks that are not negligible.
In particular, with prior art apparatus, there is a risk during the compression step of the nail going through the cortex of the calcaneus adjacent to the sole and projecting from the sole face.
With such an apparatus, the surgeon must take particular care not to apply excessive compression to the joint. Such a constraint constitutes a non-negligible drawback for the surgeon, particularly since it is often difficult or even impossible with prior art apparatus to monitor accurately the magnitude of the compression.
Furthermore, the use of apparatus of the prior art can lead to damage to the soft tissue of the face of the sole, tissue situated between the compression bearing surface and the calcaneus.
If the intensity of compression is too great, then the pressure exerted by the bearing surface can lead to necrosis of the skin on the heel.
Furthermore, fastener screws are mounted in the calcaneus and the talus after the compression step, i.e., after the talus and the calcaneus have moved relative to the tibia, so the fastener screws are poorly positioned in the bone, i.e., they can be positioned too close to the periphery of the bone or even positioned in the junction zone between two bones. An arthrodesis nail fastened in that way can then no longer hold the joint correctly.